1. Field of the Invention
The present invention relates to a synthetic resin magnet composition composed by mixing and dispersing magnetic powder to a resin binder, and suitably used as a material for molding molded-products such as magnetic rollers used in electro photograph devices or electrographic recording devices. The present invention also relates to synthetic resin magnet molded-products, such as magnetic rollers, parts for motors or magnetic sensors, molded by using the above-mentioned composition. Specifically, the present invention relates to a synthetic resin magnet composition which, when molded such as by injection, extrusion or compression, is improved in flowability in molten-state and in moldability, permits increase in the amount of magnetic powder being filled, and also, has an improved magnetic characteristic; and further relates to synthetic resin magnet molded-products using such a composition.
2. Description of the Related Art
Conventional electro photograph devices and electrographic recording devices, such as copying machines or printers, have been provided with a magnetic roller molded from a synthetic resin magnet within a rotating sleeve, which roller being provided as a developer-roller capable of making visible electrostatic latent images retained on a latent image holder such as a photosensitive drum. For such devices, there have been known developing methods for supplying toner to the surface of the latent image holder and making the latent images visible by means of a so-called xe2x80x9cjumping-development phenomenon,xe2x80x9d wherein a magnetic developing agent (i.e. toner) carried on the surface of the sleeve jumps (transfers) onto the latent image holder by virtue of the magnetic characteristic of the magnetic roller.
Conventionally, the above-described magnetic rollers have been produced by molding a synthetic resin magnet composition, which is formed by mixing a magnetic powder in a thermoplastic resin binder, into a roller-like shape and polarizing it to impart a desired magnetic characteristic thereto, by means of injection-molding or extrusion-molding in a metal mold surrounded by a magnetic field.
Further, with the advancement of the electro photograph devices and other such devices in the recent years, there has been a tendency to demand for the magnetic rollers to possess a more complicating magnetic force pattern. In order to respond to these demands, a plurality of magnet pieces, polarized to have a magnetic polarity according to the desired magnetic force pattern, has been molded from the above-mentioned synthetic resin magnet composition, and these pieces have been adhesively attached together onto the periphery of a shaft to thus create the desired magnetic force pattern.
As for the synthetic resin magnet molded-product such as the magnetic roller, a synthetic resin magnet composition is used which is molded by methods such as injection, extrusion or compression molding. Here, the composition is produced by mixing and kneading magnetic powder, such as ferrites or rare-earth magnets, to a thermoplastic resin such as polyamide resin (such as polyamide-6 or polyamide-12) and polypropylene or other such materials, which resin being used as a main binder.
With the speedup and improvement in precision of the electro photograph devices and electrographic recording devices brought about in the recent years, a demand for a higher magnetization has been rising in the synthetic resin magnet molded-products which are produced by mixing and kneading magnetic powder of ferrites, rare-earth magnet powder or other such materials to a thermoplastic resin such as polyamides used as a main binder. In order to respond to such a demand, there have been made various attempts to increase the amount of magnetic powder being filled to the synthetic resin magnet composition. However, when the amount of magnetic powder being filled is increased, deterioration in both flowability in molten-state and moldability becomes a problem. For this reason, the amount of magnetic powder being filled cannot be increased, and thus, it is difficult to improve the magnetic characteristic of the composition.
Accordingly, it is an object of the present invention to solve all of the above-mentioned problems, and to provide a synthetic resin magnet composition that can maintain its good melt flowability even when the amount of magnetic powder being filled is increased without deterioration in moldability or in uniformity of magnetic force, and thus, can accomplish the improvement in magnetic characteristic of the molded-product. A further object is to provide a synthetic resin magnet molded-product, such as a magnetic roller, that can achieve high-magnetization without causing any variation in surface magnetic force or deterioration in dimensional precision by using the above-mentioned synthetic resin magnet composition.
As a result of assiduous considerations for solving the above-mentioned problems, the present inventors have come to complete the present invention upon the discovery that by adding an aromatic polyamine compound to a composition for forming a synthetic resin magnet molded-product using a thermoplastic resin as a binder, it is possible to maintain a sufficient melt flowability and an excellent moldability even when the amount of magnetic powder filled is increased; and because the amount of magnetic powder filled can be increased, it becomes possible to realize a higher magnetization compared to conventional ones.
That is, a synthetic resin magnet composition according to one aspect of the present invention is characterized in that it is composed by mixing and dispersing a magnetic powder and at least one type of aromatic polyamine compound in a synthetic resin binder.
In the synthetic resin magnet composition of the present invention, it is preferable that the aromatic polyamine compound is either a compound represented by the following formula: 
(wherein R is a single bond or a lower alkylene group); or a compound obtained by reacting at least one compound with the above formula with an ether compound having at least one epoxy-group. Further, it is preferable that the ether compound is either a compound represented by the following formula: 
(wherein R1 is an alkylene, a cycloalkylene or an arylene group, each of which may have a substituent); or a compound represented by the following formula: 
(wherein R2 is an alkyl, a cycloalkyl or an aryl group, each of which may have a substituent). Furthermore, it is preferable that the amount of the aromatic polyamine compound being added is within a range of 0.1-10 wt %.
Further, it is preferable that in the synthetic resin magnet composition of the present invention, the magnetic powder is surface-treated with either a silane coupling agent or a titanate coupling agent; and it is preferable that the resin binder is a polyamide resin.
A synthetic resin magnet molded-product of the present invention is characterized in that it is formed by molding the above-mentioned synthetic resin magnet composition into a desired shape.